I disagree, don’t ask your girlfriend if it’s meant to be a positive thing or not. It’s up to you! How does it make you feel when she says it? Personally when people tell me my stutter is cute it feels demeaning. Even if they don’t mean to be hurtful, sometimes it is. I feel that way when people finish my sentences, I know it’s good intended but it still makes me feel crummy. You are in control of how people you care about treat you. If it doesn’t make you feel good, then tell her! If you don’t tell her, she has no way of knowing.